Of all the myriad new rules and regulations facing the hedge fund industry, one of the lesser-known is one of the bigger headaches for the industry.

According to a new poll from DMS Offshore Investment Services, new rules regarding the Foreign Account Tax Compliance Act worry more U.S. hedge funds than any other new regulations—including registration with the Securities and Exchange Commission and Commodities Futures Trading Commission, tough new European Union rules and oversight of registered investment advisors.

The poll asked U.S. hedge fund directors which new rules and regulations most worried their fund sponsors. Some 38% picked FATCA, which requires the disclosure of some foreign assets to the Internal Revenue Service, as the single thing they were most worried about. CFTC registration was cited by 26% of respondents, while just 18% said SEC registration and oversight, and the same number the Alternative Investment Fund Managers Directive.

"The last few years have been unprecedented by way of regulatory oversight—especially for U.S. hedge fund managers," Derek Delaney, who participated in the poll, said. "There managers went from light regulation to having to comply with significant new regulations, reporting requirements and government oversight. This stretched many investment managers from an operation support perspective."

DMS also asked about changes to due-diligence procedures. More than six in 10 respondents said interviews with institutional investors were the biggest change to their process last year, with transparency and regulatory oversight and accountability the biggest concerns expressed by investors in due-diligence inquiries.